1. Field of the Invention
The invention generally relates to digital television. More specifically, the invention is related to systems and devices that receive terrestrial (over-the-air) broadcast of digital television signals.
2. Background
For a variety of reasons, it may be difficult for a digital television (DTV) receiver to acquire a useable DTV signal over the air. One reason for this is multipath distortion of the broadcast signal that occurs in areas with many obstructions, such as urban areas with numerous buildings. In analog televisions, poor reception of a broadcast signal results in a degraded, but nevertheless viewable, picture. In contrast, when a DTV experiences poor reception of the broadcast signal, the result is no picture whatsoever for the end user. In this sense, DTV signal reception presents an “all or nothing at all” proposition.
In the United States, analog television broadcasts are scheduled to end by Feb. 17, 2009. It is nevertheless anticipated that there will still be a large population of television viewers relying on terrestrial broadcasting for TV viewing at that time. This population will include owners of older analog televisions, who will be required to obtain a special analog-to-digital conversion box to receive DTV broadcast signals when analog broadcasts are turned off. For members of this population, an inability to adequately receive DTV broadcast signals will mean the inability to view any television whatsoever.
In view of this, many DTV receivers are being implemented to work with so-called “smart antennas” that are intended to optimize reception of DTV signals. Smart antennas have been designed to comply with the Consumer Electronics Association (CEA) Antenna Control Interface Standard (EIA/CEA-909), which provides a standard physical interface and control protocol by which a DTV receiver can automatically adjust antenna operating parameters. Such operating parameters include, for example, electronic or mechanical steering of antenna directivity, preamplifier gain, and antenna polarization. Consumers can use smart antennas to simplify their off-air DTV experience by eliminating the need to manually adjust the antenna to receive a clear picture.
During setup of a DTV, the DTV receiver will need to perform a channel scan of all 68 radio frequency (RF) channels (channels 2-69) to try to lock on a usable signal for each channel. This process can take quite a long time and thus create frustration for consumers first setting up their DTVs.
In a DTV system that uses a smart antenna, the setup process can be particularly time-consuming. In such a system, for each channel the setup process involves setting the tuner to the appropriate channel frequency and then sending a series of configuration commands to the smart antenna to try and find an antenna mode that receives, or optimally receives, a broadcast signal. In Mode A operation in accordance with EIA/CEA-909, seven control bits are used to control antenna operation (2 bits for coarse direction or switching control, 2 bits for fine direction control, 1 bit for polarization control and 2 bits for preamplifier gain), corresponding to 128 different possible configuration commands. Thus, a DTV receiver operating in this mode may need to send up to 128 configuration commands to the antenna for each channel.
In a situation where no broadcast signal is available, the DTV receiver will need to cycle through all 128 configuration commands before it recognizes that the scan for that particular channel has failed. In the worst case, a DTV receiver that is not capable of receiving any broadcast channels whatsoever will be required to cycle through all 128 antenna configurations for each of the 68 broadcast channels, resulting in a scan of 8704 different channel/antenna combinations. In a situation where the DTV receiver allows approximately 0.5 seconds for a channel lock to occur, this process can take over an hour to complete. Moreover, this lengthy process will have to be repeated any time the smart antenna is intentionally or unintentionally moved, since the stored antenna configuration parameters for each channel will no longer be valid. Thus, a consumer who accidentally jostles an indoor antenna or has an outdoor antenna that is moved due to a storm or some other event will be forced to perform the lengthy channel scan all over again.
What is needed, then, is a technique that allows a DTV receiver to perform a channel scan in a manner that is faster and more efficient than conventional channel scanning techniques. Ideally, the desired technique should allow the DTV receiver to perform a scan of only those channels that are known to be available within a local terrestrial broadcast region. Additionally, the desired technique should allow a DTV receiver that operates in conjunction with an antenna, such as a smart antenna designed to comply with EIA/CEA 909, to use the same antenna configuration parameters for different terrestrial broadcast signals in an instance where such signals are known to originate from the same antenna location.